Metal-insulator transition in monolayer MoS$_2$ via contactless chemical doping

TL;DR

This study demonstrates a contactless doping method to induce a metal-insulator transition in monolayer MoS$_2$ by intercalating oxygen and europium under graphene, enabling electronic property tuning without chemical alteration.

Contribution

It introduces a non-invasive technique to control the electronic phase of monolayer MoS$_2$ via substrate charge modulation, including a giant band gap reduction and a metal-insulator transition.

Findings

Oxygen intercalation shifts Fermi level by 0.45 eV.

Europium intercalation induces a metal-insulator transition.

1D states in mirror-twin boundaries remain intact despite metallic transition.

Abstract

Much effort has been made to modify the properties of transition metal dichalcogenide layers via their environment as a route to new functionalization. However, it remains a challenge to induce large electronic changes without chemically altering the layer or compromising its two-dimensionality. Here, a non-invasive technique is used to shift the chemical potential of monolayer MoS$_2$ through p- and n-type doping of graphene (Gr), which remains a well-decoupled 2D substrate. With the intercalation of oxygen (O) under Gr, a nearly rigid Fermi level shift of 0.45 eV in MoS$_2$ is demonstrated, whereas the intercalation of europium (Eu) induces a metal-insulator transition in MoS$_2$, accompanied by a giant band gap reduction of 0.67 eV. Additionally, the effect of the substrate charge on 1D states within MoS$_2$ mirror-twin boundaries (MTBs) is explored. It is found that the 1D nature of the MTB states is not compromised, even when MoS$_2$ is made metallic. Furthermore, with the periodicity of the 1D states dependent on substrate-induced charging and depletion, the boundaries serve as chemical potential sensors functional up to room temperature.